The present invention relates to a sustained release pheromone-containing preparation which is used to control the proliferation of harmful insects through disturbance of the copulative communication thereof.
Recently, pheromones have been attracted special interest as substances having an effect of controlling the proliferation of harmful insects. Among these, the sex pheromones have most widely been used as the pheromones capable of being easily used and having a strong effect of inhibiting proliferation of harmful insects. The sex pheromone is a signal substance which is released by an insect in order to attract the insect of the other sex upon copulation. The pheromones have not been able to be used for controlling harmful insects until pheromones having structures quite similar to those of the naturally occurring substances can be synthesized.
There has been known the communication-disturbing method as a means for controlling the breeding of harmful insects. The term "communication-disturbing method" herein used comprises distributing a sustained release pheromone-containing preparation in fields to thus lower the ability of male or female insects to recognize the individual opposite sex and to confirm the positions thereof and to thereby inhibit copulation of the insects.
The sustained release pheromone-containing preparation must satisfy the following requirements. That is, it can release a sex pheromone in a desired amount over a desired period of time; the amount of the released pheromone per unit time is uniform throughout the releasing time; and the whole pheromone contained therein can be released within a predetermined period of time. In addition, it is sometimes required for the pheromone-containing preparation to satisfy such a requirement that it should be formed into fine particles or a suspension in order to improve the operations for spraying and application.
Examples of such sustained release pheromone-containing preparations which can satisfy the foregoing requirements include those prepared by mixing a pheromone with an inorganic substance, adding a binder to the resulting mixture and then subjecting it to granulation as disclosed in Japanese Patent Provisional Publication No. 59-139301; those comprising a pheromone which is encapsulated into micro-capsules as disclosed in U.S. Pat. No. 2,800,457, U.S. Pat. No. 2,800,458 and U.S. Pat. No. 3,577,515; and those comprising a pheromone impregnated into a polymer resin as disclosed in U.S. Pat. No. 4,111,684, U.S. Pat. No. 3,639,306 and U.S. Pat. No. 4,962,170.
Among these, the pheromone-containing preparations which are prepared by mixing a pheromone with an inorganic substance and then formed into granules cannot uniformly release the pheromone contained therein. Moreover, they have a particular external shape and therefore, they require the use of a specific spraying machine for distributing them over a wide area. In case of the sustained release pheromone-containing preparations which comprise pheromones encapsulated into micro-capsules, it is impossible to control the release rate of a sex pheromone by reducing the release surface area per unit weight thereof since the microcapsules having a diameter of not less than 0.2 mm cannot be prepared due to the technical limit in the production thereof. Moreover,the capsule covering the surface of the preparation also has low mechanical strength. For this reason, the sustained release pheromone-containing preparations which have widely been used comprise polymer resins impregnated with pheromones.
An example of the sustained release pheromone-containing preparations which comprise polymer resins impregnated with pheromones comprises a pheromone which is loaded on polymer powder. The preparation comprising a pheromone loaded on polymer powder has a large surface area per unit weight of the pheromone. Therefore, the amount of the released pheromone goes to excess in case of such a preparation and therefore, the preparation is effective over a very short period of time. Moreover, the pheromone-containing preparation undergoes the blocking phenomenon in which particles present on the surface of the preparation cause surface migration to thus adhere to one another due to, for instance, an increase in the storage temperature. As a means for preventing the blocking phenomenon, Japanese Patent Provisional Publication No. 64-208532 discloses a sustained release pheromone-containing preparation in which the pheromone is admixed with powder of a polymer resin carrying hydrophilic hydroxyl groups. Moreover, Japanese Patent Provisional Publication Nos. 56-148402 and 6-192024 each discloses a sustained release pheromone-containing preparation in which a powdery resin is adhered to the surface of the particles of the preparation. As has been discussed above, it is inevitable that the preparation must be subjected to a secondary processing in order to prevent the blocking phenomenon.